README.md

js-schema

js-schema is a new way of describing object schemas in JavaScript. It has a clean and simple syntax,
and it is capable of serializing to/from the popular JSON Schema format. The typical use case is
declarative object validation.

Usage

Include js-schema in your project with var schema = require('js-schema'); in node.js or with
<script src="js-schema.min.js"></script> in the browser. AMD module loading is also supported.

The first parameter passed to the schema function describes the schema, and the return value
is a new function called validator. Then the validator can be used to check any object against
the described schema as in the example above.

There are various patterns that can be used to describe a schema. For example,
schema({n : Number}) returns a validation function which returns true when called
with an object that has a number type property called n. This is a combination of the
object pattern and the instanceof pattern. Most of the patterns are pretty intuitive, so
reading a schema description is quite easy even if you are not familiar with js-schema.
Most patterns accept other patterns as parameters, so composition of patterns is very easy.

Extensions are functions that return validator by themselves without using the schema function
as wrapper. These extensions are usually tied to native object constructors, like Array,
Number, or String, and can be used everywhere where a pattern is expected. Examples
include Array.of(X), Number.min(X).

For serialization to JSON Schema use the toJSON() method of any schema (it returns an object)
or call JSON.stringify(x) on the schema (to get a string). For deserialization use
schema.fromJSON(json). JSON Schema support is still incomplete, but it can reliably deserialize
JSON Schemas generated by js-schema itself.

Patterns

Basic rules

There are 10 basic rules used for describing schemas:

Class (where Class is a function, and has a function type property called schema)
matches x if Class.schema(x) === true.

Class (where Class is a function) matches x if x instanceof Class.

/regexp/ matches x if /regexp/.test(x) === true.

[object] matches x if x is deep equal to object

[pattern1, pattern2, ...] matches x if any of the given patterns match x.

schema.self references the schema returned by the last use of the schema function.
For details see the self-referencing subsection.

The order is important. When calling schema(pattern), the rules are examined one by one,
starting with the first. If there's a match, js-schema first resolves the sub-patterns, and then
generates the appropriate validator function and returns it.

Example

The following example contains patterns for all of the rules. The comments
denote the number of the rules used and the nesting level of the subpatterns (indentation).

x doesn't have a property called e, or it does but it is null or undefined,
or it is an object that matches this schema

The object pattern

The object pattern is more complex than the others. Using the object pattern it is possible to
define optional properties, regexp properties, etc. This extra information can be encoded in
the property names.

The property names in an object pattern are always regular expressions, and the given schema
applies to instance properties whose name match this regexp. The number of expected matches can
also be specified with ?, + or * as the first character of the property name. ? means
0 or 1, * means 0 or more, and + means 1 or more. A single * as a property name
matches any instance property that is not matched by other regexps.

An example of using these:

var x = { /* ... */ };
var validate =schema({
'name':String, // x.name must be string'colou?r':String// x must have a string type property called either// 'color' or 'colour' but not both'?location':String, // if x has a property called 'location' then it must be string'*identifier-.*':Number, // if the name of a property of x matches /identifier-.*/ then// it must be a number'+serialnumber-.*':Number, // if the name of a property of x matches /serialnumber-.*/ then// it must be a number and there should be at least one such property'*':Boolean// any other property that doesn't match any of these rules// must be Boolean
});
assert( validate(x) ===true );

Self-referencing

The easiest way to do self-referencing is using schema.self. However, to support a more
intuitive notation (as seen in the Tree example above) there is an other way to reference
the schema that is being described. When executing this:

js-schema sees in fact { left : [ Number, undefined ], right : [ Number, undefined ] } as first
parameter, since the value of the Tree variable is undefined when the schema function is
called. Consider the meaning of [ Number, undefined ] according to the rules described above:
'this property must be either Number, or anything else'. It doesn't make much sense to include
'anything else' in an 'or' relation. If js-schema sees undefined in an or relation, it assumes
that this is in fact a self-reference.

Use this feature carefully, because it may easily lead to bugs. Only use it when the return value
of the schema function is assigned to a newly defined variable.

Extensions

Numbers

There are five functions that can be used for describing number ranges: min, max, below,
above and step. All of these are chainable, so for example Number.min(a).below(b) matches x
if a <= x && x < b. The Number.step(a) matches x if x is a divisible by a.

Strings

The String.of method has three signatures:

String.of(charset) matches x if it is a string and contains characters that are included in charset

String.of(length, charset) additionally checks the length of the instance and returns true only if it equals to length.

String.of(minLength, maxLength, charset) is similar, but checks if the length is in the given interval.

charset must be given in a format that can be directly inserted in a regular expression when
wrapped by []. For example, 'abc' means a character set containing the first 3 lowercase letters
of the english alphabet, while 'a-zA-C' means a character set of all english lowercase letters,
and the first 3 uppercase letters. If charset is undefined or null then there's no restriction on
the character set.

Arrays

The Array.like(array) matches x if x instanceof Array and it deep equals array.

Array.of(length, pattern) additionally checks the length of the instance and returns true only if it equals to length.

Array.of(minLength, maxLength, pattern) is similar, but checks if the length is in the given interval.

Objects

Object.reference(object) matches x if x === object.

Object.like(object) matches x if x deep equals object.

Functions

Function.reference(func) matches x if x === func.

Future plans

Better JSON Schema support. js-schema should be able to parse any valid JSON schema and generate
JSON Schema for most of the patterns (this is not possible in general, because of patterns that hold
external references like the 'instanceof' pattern).

Contributing

Feel free to open an issue or send a pull request if you would like to help improving js-schema or find a bug.

Installation

Build

To build the browser version you will need node.js and the development dependencies that can be
installed with npm (type npm install ./ in the project directory). build.sh
assembles a debug version using browserify and then minifies it using uglify.